1. Field of the Invention
The present invention relates to separable electrical connectors and more particularly to improvements in separable electrical connectors such as loadbreak connectors and deadbreak connectors, including a sleeve of low coefficient material for ease of connection/disconnection and which includes vents to prevent flashover upon switching (opening) the connectors.
2. Description of the Prior Art
Loadbreak connectors used in conjunction with 15 and 25 KV switchgear generally include a power cable elbow connector having one end adapted for receiving a power cable and another end adapted for receiving a loadbreak bushing insert. The end adapted for receiving the bushing insert generally includes an elbow cuff for providing an interference fit with a molded flange on the bushing insert. This interference fit between the elbow cuff and the bushing insert provides a moisture and dust seal therebetween. An indicator band may be provided on a portion of the loadbreak bushing insert so that an inspector can quickly visually determine proper assembly of the elbow cuff and the bushing insert.
The elbow cuff forms a cavity having a volume of air which is expelled upon insertion of the bushing insert. During initial movement of the loadbreak connectors in the disassembly operation, the volume of air in the elbow cavity increases but is sealed off at the elbow cuff resulting in a decrease in pressure within the cavity. The dielectric strength of the air in the cavity decreases with the decrease in air pressure. Although this is a transient condition, it occurs at a critical point in the disassembly operation and can result in dielectric breakdown of the opening interface causing a flashover or arc to ground. The occurrence of flashover is also related to other parameters such as ambient temperature, the time relationship between the physical separation of the connectors and the sinusoidal voltage through the loadbreak connectors.
Another reason for flashover while switching loadbreak connectors, prior to contact separation, is attributed to a decrease in dielectric strength of the air along the interface between the bushing insert and the power cable elbow to ground. As earlier described, a decrease in air pressure is momentarily formed by the sealed cavity between the elbow cuff and the bushing insert flange. The lower pressure in the cavity reduces the dielectric strength of the air along the connection interface possibly resulting in flashover.
Another drawback with loadbreak connectors of the prior art is the difficulty involved in inserting one end of the loadbreak bushing insert into the power elbow connector and inserting the opposite end of the loadbreak bushing insert into a bushing well. In particular, because the interface surfaces of the loadbreak bushing insert and the power elbow connector and the bushing well are typically made from a rubber material, the frictional forces engaged in inserting the loadbreak bushing insert are substantial, even when lubricated. In other words, the rubber to rubber surfaces typically stick together upon assembly of the loadbreak connector.
Accordingly, it would be advantageous to design a loadbreak connector system including a power cable elbow and a loadbreak bushing insert which reduces or prevents the possibility of a flashover upon switching of the connectors. It would also be desirable to provide a loadbreak connector system which is easily assembled and quickly visually inspected to determine proper assembly of the elbow cuff and the bushing insert. It would further be advantageous to provide such a system with a visible identification of the operating voltage class of the connectors.